Inflammation is increasingly recognized as a key feature of sickle cell disease, potentially linking vaso-occlusion, endothelial cell dysfunction, reactive airway disease and pulmonary hypertension. Acutely, inflammation is triggered by hypoxia-reperfusion injury resulting from vaso-occlusion;chronically, it is sustained by the abnormal cytokine milieu perpetuated by chronic hypoxia and by release of placenta growth factor, a strong proinflammatory molecule released from the stimulated erythron in sickle cell disease. We show that placenta growth factor increases leukotriene synthesis via upregulation of 5-lipoxygenase, which catalyzes production of leukotrienes. Leukotrienes are among the most potent proinflammatory molecules for polymorphonuclear cells, and increase airway hyperreactivity, vascular leak, and edema. Chronic leukotriene elevation has been also shown to be associated with pulmonary hypertension and fibrosis. We propose to block leukotriene synthesis with a 5-lipoxygenase inhibitor, zileuton. We postulate that inhibition of LT production by zileuton will be safe, feasible and significantly reduce inflammation, airway hyperreactivity, improve HbF and secondarily reduce acute sickle events. A two-step approach is proposed: (1) A limited Phase I pilot study will address the safety of zileuton in children (12-18 yrs of age) and adults (18 years and older) with sickle cell disease. While zileuton is FDA approved for asthma in individuals 12 years or older, it has not been studied in the sickle population, nor has it been studied primarily for its anti-inflammatory effects in this disease. The Phase I component will therefore determine a safe dose of zileuton in sickle cell disease that has a biological effect on inflammatory endpoints and compare zileuton and leukotriene pharmacokinetics to published data on normal individuals and patients with asthma. (2) A randomized;double-blind, placebo-controlled crossover Phase II trial will determine the feasibility of chronic zileuton administration and its effect on inflammatory markers as primary endpoints. Secondary endpoints will be acute sickle events, Hb F levels, pulmonary function, and markers of pulmonary hypertension. Inflammation and pulmonary disease are two strong predictors of sickle cell disease severity and mortality. Zileuton may affect both these aspects and have an overall positive impact on disease morbidity. Lay Summary: Inflammation and lung disease are important features of sickle cell disease. This study will test the ability of Zileuton, an anti-inflammatory drug licensed for treatment of asthma, to reduce inflammation in sickle cell disease and improve lung function.